Many journeys come up as favourites for me, a brief list:
Swansea > Swindon > Penzance and back via same route on 21st May 2004. An awesome journey and all in complimentary First Class. Wish I had been bashing back then, I'd have known what power cars I had on the day. If anyone has HST gen from that day, then please PM me.
Kings Cross to Inverness and back the following day with 43006+43008. An excellent experience to be on what was then (and AFAIK still is) the longest HST-operated service in the country. A fantastic performance from both power cars and a journey that I'll never forget.
Manchester > Newquay via Styal, Crewe, Alsager, Stoke-on-Trent, Stafford, New Street then the Camp Hill line before returning as far as Bristol Parkway. Extreme bit of miles and a stunning performance from 43046+43083 in May 2007. Without a shadow of a doubt, an excellent day for mileage and red-penning some track for HST coverage, and all in FC from Crewe to Newquay!
Kings Cross to Sunderland and back on 30th January 2010 with 43065+43123. Stunning performance from both power cars and will possibly be the last time I scoop two winners on the same set and for decent mileage.
Crewe to Fort William with the Jacobite onwards to Mallaig. An amazing journey and one I'd love to do again. London Euston to Oban on the diverted sleeper in February 2006 was great, as was the HST from Edinburgh to York via Ferryhill and Stockton on the way back home.
Hereford to Paddington in December 2006 was a great journey, awesome thrash from 43036 on the front (forgotten what was on the back), all enjoyed in FC throughout. The birthday bash around London afterwards was also great fun, although 180113 on the 1242 Paddington to Hereford the day after was NOT fun, not even in FC, mainly due to expecting a HST and to have no buffet crew all the way home was punishing.
Swansea to Paddington is also a favourite journey of mine from those in my enthusiast past. So many times I did that journey in both directions, but the best ones involved the 1130 Swansea to Paddington, as it had the Pullman dining service on it. I used that so often the crew knew what my order was before I had chance to tell them!
Bristol to Weymouth and back in September 2009 will always rate as one of the best bashes of all-time. First trip to the Southern Region with 37s and a winner in the form of 37670. Stunning performance from both beasts on the day, will never forget the scrum for the front door as the set rolled in for the return journey!
Bristol to Brighton in October 2004 was a stunner in terms of sheer randomness with the 31s, as well as the VEP(?) from Brighton to Portsmouth and CIG back to Fratton. Shame about having to suffer a 158 all the way back to Cardiff that night
Crewe to Holyhead in June 2004 (I think) with 47810 on an Euston to Holyhead was just awesome. Not ever likely to forget poor James missing the thrash and clag away from Colwyn Bay!
Crewe to Chester, believed to be in April 2004, with 43068+43121. Not a long journey, but the only time I managed to get on-board a Virgin HST. Shame I then had to bail for a 153 to Crewe for 158829 back to at least Newport for something decent back to Swansea, as I had to go try on wedding suits for my eldest sister's wedding!
All journeys along the Heart of Wales line. Stunning scenery and always a good ride.
158714 from Inverness to Kyle in declassified FC for a SRPS tour with 47245+47851 back to Dalmeny was lovely. Stunning scenery and would love to do it again one day.
2026 Aberdeen to Edinburgh via Cowdenbeath and the Edinburgh Suburban line in December 2008 with 43357 (winner!) and 43285 was a great journey for the winner power car, new all-time territory and for HST coverage (obviously), the following morning getting a winner 67009 to Westerton (didn't enjoy the non-working ETS though :roll

and all-time required track and 314s in Glasgow was great, before a boring journey back with Megabus to Manchester. Was a good excuse for some doss though!
Scooping the Joint Line on NXEC diversions in November 2008 was also quite fun, especially getting 43056 back. Won't soon forget the thrash up through Lincoln on the northbound journey! Scooping winner track the following morning (Copley Hill chord?) in Leeds was excellent too and with 43052+43082
That's about all I can think of for now
